Forward Communication Only Placements and Their Use for Parallel Program Construction

The context of this paper is automatic parallelization by the space-time mapping method. One key issue in that approach is to adjust the granularity of the derived parallelism. For that purpose, we use tiling in the space and time dimensions. While space tiling is always legal, there are constraints on the possibility of time tiling, unless the placement is such that communications always go in the same direction (forward communications only). We derive an algorithm that automatically constructs an FCO placement – if it exists. We show that the method is applicable to many familiar kernels and that it gives satisfactory speedups.

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